1. Field of the Invention
This invention relates to process and apparatus for producing ethylene from ethane, and more particularly to the production of ethylene by the oxidative dehydrogenation of ethane.
2. Description of the Prior Art
Processes have been developed for producing ethylene from ethane wherein ethane, oxygen and either elemental chlorine or a chlorine-containing reactant (e.g. HCl) are passed in contact with a catalyst at elevated temperatures for autothermic cracking (i.e., oxidative dehydrogenation) of ethane. See, e.g., U.S. Pat. Nos. 3,217,064; 3,278,627; 3,278,629; 3,278,630; 3,278,631; 3,308,183; 3,308,197; 3,658,933; 3,658,934; 3,702,311; and 3,862,996. The reaction of chlorine, oxygen and ethane to form ethylene, hydrogen chloride and water may be illustrated by the following equation: EQU C.sub.2 H.sub.6 + 1/2 Cl.sub.2 + 1/4 O.sub.2 .fwdarw. C.sub.2 H.sub.4 + HCl + 1/2 H.sub.2 O
while such processes produced ethylene, the conversions are typically low, requiring recycle of large amounts of unreacted ethane, thereby leading to increased equipment costs and processing expenses. In addition, use of catalyst entails added expense due to the cost of the catalyst and to the need to periodically replace catalyst which has become poisoned or otherwise inactivated as a result of impurities present in the feed streams or from various by-products formed in the reaction. While processes such as that disclosed in U.S. Pat. No. 3,336,412 have been developed which do not employ catalyst, the pyrolysis product generally contains a substantial quantity of acetylene, thereby complicating downstream recovery of the ethylene that is produced.
While generally less than about 1 weight percent of ethane fed to the reactor is converted to carbon, and thus while carbon formation does not seriously reduce the yield of ethylene, carbon depositions are disadvantageous due to the plugging of the reactor and downstream recovery equipment. While we do not wish to be limited by the theory given below, we believe that the carbon formation results from polymerization of acetylene which is in turn formed by the cracking of ethylene. The acetylene polymerization leads to formation of straight chains of increasing length whose condensation will ultimately form conjugated ring structures. Successive conjugations to form larger and larger conjugated ring structures at nucleation sites will ultimately lead to turbostratic carbon with platelets adhering to and aligned with the walls of reactor and exit lines. Continued growth of the straight chain acetylene polymers and homogenous dehydrogenation is believed to lead to amorphous carbon which is entrained in exit gases.
Thus, a process is desired which will provide ethylene from ethane while decreasing the amount of carbon deposit on process equipment.
Belgium Pat. No. 821,397, filed Oct. 23, 1974, discloses a process for preparation of ethylene dichloride and vinyl chloride from ethylene wherein the ethylene is produced by the autothermic cracking of ethane.